1. Field of the Invention
This disclosure relates to the field of register systems for rotary presses, particularly for the registration of plate cylinders in newspaper presses.
2. Description of the Related Art
FIG. 1 shows a general layout of a portion of an exemplary press line (100) as might be used in any major newspaper to print pages which are primarily black and white with so-called “spot” color or occasional full color pages. The press line (100) includes at least one press unit (101), a series of angle bars (111) and a folder (121). While the press line of FIG. 1 shows two press units (101), one set of angle bars (111) and a single folder (121), most press lines will have a folder (121) and two sets of angle bars (111) with between 4 press units (101) to 10 press units (101) depending on the desired capacity and design of the press line (100). Further, a single press room may have one or more than one press line, again depending on capacity and design. The press lines may operate independently, or may operate in conjunction with each other. For the purpose of this disclosure, it will be presumed that the press line include at least one press unit (101) and any other associated structure necessary which operates in the standard manner known to those of ordinary skill in the art.
The press units (101) may be any type of press unit (101) but will generally be either standard units (103), three color units (105) (which is usually a standard unit (103) with a half deck unit (115) placed thereon), four color units (which is usually a standard unit (103) with a full deck unit (not shown) placed thereon) or tower units (not shown). The half deck (115) shown would be considered a “13 side” half deck based on its arrangement, a “10 side” half deck would be considered essentially interchangeable and would be arranged in a mirrored position. The type of press unit (101) depends upon the flexibility originally built into the press line (100). A pure black and white press line (100), for instance, will generally only have standard units (103), while a press line (100) utilizing some color (spot or process color) may have some three color units (105), four color units and/or towers. Full color press lines or press lines designed to be highly versatile, may comprise all tower press units.
Regardless of the exact press units (101) used, the press line will generally operate in a similar fashion. Paper (131) will be fed from a paper roll to the press units (101), generally from underneath the press units (101). The paper (131) will be of a predetermined width and will generally be provided on a large diameter roll containing a length many times greater than the height of any particular newspaper page. The page will generally be printed upright so that if the roll of paper is viewed before cutting, there will be a predetermined number of pages arranged side to side across the width of the roll, with the same pages repeated serially down the roll as it unwinds and is printed. The exact width of the paper roll is selected based on the width of the press unit (101) and the desired size of the resultant pages.
As the paper (131) comes up through the press unit (101), ink and dampener solution are transferred from various troughs or other storage devices onto a series of transfer rollers. Eventually the ink and dampener solution are applied to a plate cylinder (10) or (13). While the term “cylinder” is used for some components while “roller” or “drum” is used for others, this is done for convenience and does not imply any structure to any component which could not be encompassed through the use of a different term. Plate cylinder (10) or (13) includes the necessary structure to allow for the ink to be placed into the correct format so as to form the necessary text or images to be printed. This may be the actual shape to be printed (as would be the case in offset lithography) or may be a reverse image. The plate cylinder (10) or (13) then transfers the ink to blanket cylinder (11) or (12) (forming a reverse image in offset lithography) which then transfers the ink to the paper (131) printing the page. Both sides of the page are generally printed simultaneously by the two blanket cylinders (11) and (12) in a standard press unit (103). If a three color press unit (105) is used, the paper (131) may be routed past an additional plate cylinder (1801) and blanket cylinder (1800).
It is important to note that the reference numbers chosen for the plate (10), (13), and (1801) and blanket (11), (12), and (1800) cylinders in this disclosure were specifically chosen. Various references related to these cylinders utilizing these same reference numbers are known in the industry. Therefore, the choice of reference and depicted side implies which side of the press unit (101) is being viewed (and that the half deck discussed is a “13 side” half deck as opposed to a “10 side” half deck, although the description herein could be readily adapted to a “10 side” half deck). While the systems and methods can obviously be reversed if the system is being accessed from a different side, this use of reference numbers does help to provide for a particular indication of particular structure as generally no other distinguishing characteristics of the press unit (101) are used. In the case of FIG. 1 the choice of reference numbers shows that the view is from the operator side of the press.
Generally, the printing is accomplished by ink being transferred from the blanket cylinder (11), (12), or (1800) to the paper (131). In order to print cleanly, the paper (131) cannot be suspended over the blanket cylinder (11), (12) or (1800), but the blanket cylinder (11), (12), or (1800) must be allowed to push against a surface (generally another revolving cylinder) to transfer the ink to the paper (131) and cleanly print the page. In the standard press unit (103), the two blanket cylinders (11) and (12) push against each other printing both sides of the page simultaneously with each cylinder creating the surface for the other cylinder to push against. In the three color unit (105), there is included a common impression cylinder (48) which may be pressed against by any or all of the blanket cylinders (11), (12), or (1800) to provide the necessary surface.
Once the paper (131) has been printed by any particular press unit (101), it may be routed through additional press units (101) (or may go back through the same press unit (101) contacting different blanket cylinders) to add additional color or colors by contacting another blanket cylinder (11), (12), or (1800) and will eventually be routed through the angle bars (111).
Since color has been used in printing presses, the need for registration and alignment of a particular press unit has become important. As discussed above, a page will often go through more than one different press unit or will pass more than once through a press unit to obtain color on the page. The full color (or spot color) of a newspaper is often printed with a multiple color ink arrangement whereby a page passes over a first blanket roller to provide for a first color of ink, for instance black. That pass prints just the items which are in that color on the page and then passes by a different blanket roller which just prints the items which are of a next color, (for instance magenta). In a spot color page, this may be the end of the printing process, however, if the page is intended to be in full color (as is often the case with the front page for instance), the page may pass over other blanket cylinders (typically one for cyan and one for yellow) which each apply ink to their appropriate sections. As is well understood in the art, with these four colors (cyan, magenta, yellow, and black), virtually any color can be created as inks can be placed together on the same area (mixed) to generate an additional color (for instance cyan ink may be placed on a spot of yellow ink to make that spot green). The exact composition of each color in all the locations therefore generates the final color image. Therefore in most color pages of a newspaper, the page has passed over 4 individual blanket cylinders to generate the page.
Because these cylinders are spatially separated and may even be in separate press units, it is necessary to insure that each blanket cylinder prints the image aligned on the page in the same fashion as all the other blanket cylinders will print other colors on the same page. Further, even in a pure black and white single printing, it may be necessary to adjust alignment to make sure that pages are printed and aligned on both sides of the newspaper sheet to make sure that if small margins are used there is no damage to the text of the paper during cutting.
When the cylinders are correctly aligned and print on the correct area of the page so that the resultant picture is clear, the pressline is referred to as being in register. If presses are out of register, a color page will often have a colored “shadow” in the color of the misaligned press and the image will generally appear distorted as unintended color mixing has occurred. Even with spot color, there may be unintended lines of white paper or other color where the spot color or black ink has been misplaced.
While the term “register” is used to refer to correctly aligned presses, it is also the term used to refer to the devices which allow for adjusting of the positioning of the cylinders to correctly print the page. These registers traditionally come as two different types, each of which aligns the printing of one of the two dimensions of the page.
Generally, registration is performed on the plate cylinder as opposed to the blanket cylinder and printing adjustment is provided by slight movement of the plate cylinder of one press unit so that the position of the image printed by that press unit is aligned with a position of the images printed by the other press units. Circumferential registration adjusts the relationship of the printing up and down on the web. In particular, if a first cylinder is printing too high on the web, this means that the first cylinder is effectively printing the page too early on the web. The circumferential register allows the plate cylinder to be rotated about its circumference which effectively shifts the page upward or downward on the web and can correct the registration in this direction by changing the timing of when the page is printed on the web.
Alternatively, the page may be offset laterally. A sidelay register is used for this adjustment. A sidelay register serves to shift the plate cylinder laterally along its axis without rotating it. In this way the cylinder is shifted to print slightly left or right of its prior position on the web.
It is important to recognize that sidelay and circumferential adjustments are not intended to make gross movements with the various cylinders. They are instead intended to fine tune the placement of a particular press unit to correspond with the placement of other press units. Gross adjustments can be made using the compensator and related systems which are used to delay a page (by requiring it to travel a certain distance) before reaching the next press unit.
To perform circumferential adjustment, systems traditionally moved a plate gear which is used to rotate the plate cylinder during printing linearly on the plate cylinder axis and relative to the other gears in the drive train. In particular, by moving the plate gear along the axis of the plate cylinder, the plate gear is forced to engage in a slight rotation to stay in contact with the teeth of the mating gear in the drive train as the plate gear generally has helical teeth thereon. This in turn forces the plate cylinder to also rotate as it cannot be moved circumferentially relative to the plate gear as such relation is intended from the design. Therefore, small adjustments to the circumferential position of the plate cylinder can be made by applying a linear translation to the plate gear. To perform sidelay adjustment, the plate cylinder journal was traditionally linearly translated along its axis. In this situation, as the plate cylinder is being acted upon, the plate cylinder slides linearly.
From this general concept a number of different systems for performing registration have been proposed. All of these systems generally have a similar number of problems. In the first instance, generally a motor will not act directly to linearly move the plate gear or plate cylinder. Instead a motor acts on a gear train, chains, and sprockets that in turn generate the linear motion on the plate gear or the plate cylinder. All these systems generally have problems because regardless of how well gears, chains, and sprockets are designed, there is always some backlash in them and as gears wear the interrelated motion can become less accurate. Because the distances to be moved are generally very small while the material being moved is very large, even small amounts of backlash can provide for slop in the distance of adjustment. Further, many of these systems rely on hydraulic cylinders which have certain minimum amounts of movement distance and which may not be able to perform sufficiently small enough translations.
The problems become particularly acute when related to the operator's need to determine how far the system has moved. That is, the measurement of the change in registration due to the register's operation. Because the distances are small, an operator is generally forced to rely on mechanical display systems such as gauge needles to determine how far the plate cylinder has moved either axially or circumferentially. Traditionally, when measuring the amount that the register has been altered by the registration system, the system generally used the motion of the drive motor or even motion of hand wheels which can be determined to a fairly high degree of accuracy, the movement of the plate gear or plate cylinder was then calculated based on the expected operation of the gear train.
As should be apparent, with even a small amount of backlash in each gear in the train, the expected adjustment and the actual adjustment can be significantly different. Further, while some backlash (which is known) can be compensated for, gears wear over time and the backlash is likely to change and therefore the measurement will become less and less accurate over time. Still further, at small amounts of movement, the problem is further compounded by other influences on the movement. For instance friction or inertia from the large components may inhibit the initial movement causing flex in various objects or gears instead of actual translation. This flex may be perceived as actual translation which may result in movement being measured where there actually is none.
A still further problem results in the measurement operation of many of these systems introducing further inaccuracy. In many cases the measurement operation is separated from the actual movement gear train. In particular, the movement of the motor may be detected by having the motor both move a gear train which acts on the plate gear or plate cylinder and simultaneously act on a second gear train which acts on a dial or related device to show the action performed. As backlash between these two gear trains may be different, the measurement readout may register a different amount than the interfacing gear train actually moves. This is on top of the fact that the gear train may actually move differently from what the motor would predict.